Running and Menstrual Cycles: Impact on Periods & Weight Gain

Question
Hello,
I am 17 (female, 5'3, 130 lb., almost 18 and I have 2 'yes' or 'no' questions that I hope you can answer.

If a girl takes up running, is it more likely to make her period occur earlier than normal? or later than normal or does it not affect it at all?

My other question...is it normal for a girl to experience a 15lb. weight gain in less than a month? I've gained 15 lb. (115 lbs. to 130 lbs.) and I don't know where is phyically is. I weightlift a lot but normally I don't gain this much in a month...

Thanks,
Christine

Answer
Women who run can often skip periods.  This occurs for two possible reasons. 1. Their percent body fat drops low enough to cause the menstrual cycle to stop.  Once they gain weight and some fat back, their cycle restarts.  And 2. the endorphins that are produced by the brain can sometimes effect your menstrual cycle.  I wouldn't expect your period to come earlier.

As for your 15# weight gain, my guess is that it is mostly fluid or water.  That significant a weight gain in such a short amount of time is unlikely to be true fat.  That would be an extraordinary amount of excess calories that you'd have to accumulate.  In fact, one pound is equal to 3500 calories, so if you do the math 52,500 extra calories over the month, or about 52 extra Big Mac's.

Hope that helps.  It's a bit more than 'yes' or 'no'.